1. Field of the Invention
The present invention relates to an oil filer that includes a casing having a cylinder portion formed with an opening in one end thereof and a threaded portion formed on an inner peripheral surface of the cylinder portion, and a cap threadably engaging with the threaded portion so as to contain a filter element between the cap and the casing. Particularly, the invention relates to an oil filter mounted in a vehicle and filtering out foreign substances from oil lubricating an internal combustion engine.
2. Description of Related Art
There is known the oil filter that is mounted in the vehicle and filters out the foreign substances from the oil lubricating the internal combustion engine. There have been also proposed a variety of oil filters designed to allow for replacement of the filter element.
For example, an oil filter is disclosed in which a male thread formed on an outer peripheral surface of an cylindrical cap is screwed in a female thread formed on an inner peripheral surface of a case whereby the cap is fixed to the case (see Japanese Patent Application Publication No. 2005-180387 (JP 2005-180387 A)). In this oil filter, a gap between the case and the cap is sealed by fitting an O-ring in a mating recess formed in the cap.
However, the oil filter disclosed in the above JP 2005-180387 A has possibility that the O-ring may be erroneously mounted on the cap at a place adjoining a case-side of a flange, to which an open end of the case is abuttedly locked.
The O-ring should essentially be fitted in the mating recess formed in the cap. Even in a case where the O-ring is erroneously mounted on the cap at the place adjoining the case-side of the flange of the cap; however, the oil is sealed to some extent by the O-ring clamped between the open end of the case and the flange of the cap. In this case, an operating personnel may stay unaware of the erroneous mounting of the O-ring because the erroneously mounted O-ring is clamped between the flange of the cap and the open end of the case.